feat(doc): added introduction (#6806)

taken from https://swagger.io/tools/swagger-ui/

Author: mathis-m

README.md

@@ -10,6 +10,10 @@
 ![monthly packagist installs](https://img.shields.io/packagist/dm/swagger-api/swagger-ui.svg?label=packagist%20installs)
 ![gzip size](https://img.shields.io/bundlephobia/minzip/swagger-ui.svg?label=gzip%20size)
 
+## Introduction
+[Swagger UI](https://swagger.io/tools/swagger-ui/) allows anyone — be it your development team or your end consumers — to visualize and interact with the API’s resources without having any of the implementation logic in place. It’s automatically generated from your OpenAPI (formerly known as Swagger) Specification, with the visual documentation making it easy for back end implementation and client side consumption.
+
+## General
 **👉🏼 Want to score an easy open-source contribution?** Check out our [Good first issue](https://github.com/swagger-api/swagger-ui/issues?q=is%3Aissue+is%3Aopen+label%3A%22Good+first+issue%22) label.
 
 **🕰️ Looking for the older version of Swagger UI?** Refer to the [*2.x* branch](https://github.com/swagger-api/swagger-ui/tree/2.x).
@@ -84,4 +88,4 @@ To help with the migration, here are the currently known issues with 3.X. This l
 
 ## Security contact
 
-Please disclose any security-related issues or vulnerabilities by emailing [[email protected]](mailto:[email protected]), instead of using the public issue tracker.
+Please disclose any security-related issues or vulnerabilities by emailing [[email protected]](mailto:[email protected]), instead of using the public issue tracker.